Polylactic acid molding and process for producing the same

a technology of polylactic acid and molding process, which is applied in the field of polylactic acid formed articles, can solve the problems of poor heat resistance of molded or formed articles, low productivity of polylactic acid crystallization speed, and general less compatibility of wax employed as the crystal nucleus agent, etc., and achieve excellent heat resistance and shock resistance and high production efficiency.

Inactive Publication Date: 2005-07-28
UNITIKA LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0008] To solve the aforesaid problems, it is an object of the present invention to provide a polylactic acid formed article which is excellent in heat resistance and shock resistance and can be produced at a higher productivity by a forming process.

Problems solved by technology

Where the polylactic acid is molded or formed into a sheet or a container, however, crystals of the polylactic acid are generally completely fused due to thermal history experienced during the molding or the forming, so that the resulting molded or formed article is poor in heat resistance.
However, this method is problematic in that the crystallization of the polymer is insufficient without a heat treatment and the productivity is low with a lower crystallization speed of the polymer.
However, the wax employed as the crystal nucleus agent is generally less compatible with the polylactic acid thereby to be bled out.
Therefore, only a small amount of the wax is added, which is insufficient for formation of crystal nuclei.
However, the sheet produced by this method is a stretched sheet, which is further stretched when subjected to a forming process to provide a formed article.
Unfortunately, the sheet once stretched is inferior in drawability and, therefore, is not suitable for deep drawing.
The applications of the sheet are inevitably limited.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

example 1

[0085] First, 84% by mass of polylactic acid (NATURE WORKS available from Cargill Dow) having an optical purity of 97.6%, a residual lactide amount of 0.2% by mass and a weight-average molecular weight of 200,000, 15% by mass of talc as a crystal nucleus agent (MW HS-T available from Hayashi Kasei) having an average particle diameter of 2.75 μm and 1% by mass of erucamide (ALFLOW P10 available from Nihon yushi) as a dispersant were melt-kneaded by means of a biaxial kneader / extruder (MODEL TEX44α available from Nihon Seikosho) to prepare a polylactic acid compound material at an extrusion temperature of 230° C. With the use of a uniaxial extruder having a 1000-mm wide T-die and a screw having a diameter of 90 mm, the polylactic acid compound material was melt-extruded at an extrusion temperature of 215° C. to provide a 350 μm thick unstretched sheet in intimate contact with a cast roll set at 40° C. With the use of a single-shot indirect-heating vacuum forming machine and an aluminu...

example 2

[0087] An unstretched sheet was prepared and a container (formed article) was formed from the sheet in substantially the same manner as in Example 1, except that polylactic acid (NATURE WORKS available from Cargill Dow) having an optical purity of 92.0%, a residual lactide amount of 0.2% by mass and a weight-average molecular weight of 190,000 was employed. The heat treatment was performed at a die inside temperature of 125° C. for 15 seconds during the vacuum forming.

[0088] The properties of the resulting formed article and the like are shown in Table 1.

example 3

[0089] A container (formed article) was produced in substantially the same manner as in Example 1, except that polylactic acid (NATURE WORKS available from Cargill Dow) having an optical purity of 97.8%, a residual lactide amount of 0.4% by mass and a weight-average molecular weight of 200,000 was employed.

[0090] The properties of the resulting formed article and the like are shown in Table 1.

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Abstract

A polylactic acid formed article and a production process therefor. A resin composition for the formed article comprises polylactic acid having an optical purity of not lower than 90% and a residual lactide amount of 0.1 to 0.6% by mass, and 1 to 25% by mass of a crystal nucleus agent. The formed article is characterized in that a difference (|ΔHm|−|ΔHc|) between the absolute value of a crystal fusion heat amount ΔHm as measured at a heat-up rate of 20° C./min by means of a differential scanning calorimeter and the absolute value of a heat-up crystallization heat amount ΔHc generated by heat-up crystallization is not lower than 25 J/g, and has a crystallinity of not lower than 35% as determined by X-ray measurement and a crystallization speed of not lower than 0.05 min−1 at 130° C.

Description

TECHNICAL FIELD [0001] The present invention relates to a polylactic acid formed article and a process for producing the same. BACKGROUND ART [0002] With a recent increasing social demand for environmental conservation, biodegradable polymers which are decomposed by microorganism have attracted attention. Specific examples of the biodegradable polymers include fusion-moldable polyesters including aliphatic polyesters such as polybutylene succinate, polycaprolactone and polylactic acid, and aliphatic / aromatic copolymer polyesters such as terephthalic acid / 1,4-butanediol / adipic acid copolymers. Among these aliphatic polyesters, the polylactic acid, which is widely distributed in nature and is harmless to animals, plants and humans, is highly heat-resistant with a melting point of 140 to 175° C. The polylactic acid is promising as a less expensive thermoplastic biodegradable resin. [0003] Where the polylactic acid is molded or formed into a sheet or a container, however, crystals of th...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C08J5/00B29C51/00B29C51/10B29C51/42B29C71/02B29K67/00C08K3/34C08K5/00C08K5/20C08L67/04C08L101/16
CPCB29C51/002B29C51/10B29C71/02B29C2791/006B29C2791/007C08K3/34C08K5/20C08K5/0083C08L67/04C08G63/08C08J5/00C08J5/18
Inventor NISHIMURA, HIROSHIHIOKI, MASANOBU
Owner UNITIKA LTD
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